I don't mean this to start a political debate but the Mexican border wall discussion amuses me.
These are just my observations.
From the beginning, I wondered what they were going to do about the Rio Grande. It forms the border between Texas and 4 Mexican states. What side of the river will the wall be on? Certainly not down the middle of the river. A wall on the Mexico side would cut them off from essential water sources. It would also be trespassing. A wall on our side would cut us off from that water source. An extensive farming region near the mouth in Texas rely on it for irrigation and all the recreation now in use.
The rest of the border contains some extremely rugged terrain. Today I watched a video of an aerial view of the Big Bend region. I can't imagine a wall running up and down some of those cliffs. Areas of the Arizona/California Mexico border are pretty rugged too.
The downside would be the environmental damage from wildlife no longer being able to traverse the border. The same thing happened when the Panama Canal was built.
Isolating wildlife populations can contribute to extinctions and cause a depletion of the gene pool on one side or both.
For tens of thousands of years, the isthmus of Panama was a conduit for wildlife species to traverse to and from both continents. That ended by 1910.
As for as who pays. I don't think our fiduciary astute congress would go for it. Certainly Mexico won't.
When the Ming dynasty wanted to complete the work on the Great Wall over rugged terrain that started with the first Chinese emperor, Qin Shi Huang building sections around 200bc - they wanted it and they paid for it.
When the Communists wanted a wall separating East and West Berlin and the contiguous Iron Curtain, the East Germans paid for it and it was on their side of the border.
We apparently are going to use 2000+ year old technology at great cost to separate areas when there are modern, less expensive technological alternatives.
Why aren't we proposing a wall on the US - Canadian border? As the longest international border in the world between 2 countries, that would be a great way to spend our money. 5,500 miles would be a pretty penny. Oh, and don't forget the 1500 mile border with Alaska and Canada.
Just sayin'.